This paper describes an approach to study the diagnosability of technological systems, by characterizing their observable behaviors. Due to the interaction between many components, faults can occur in a technological system and cause hard damages not only to its integrity but also to its environment. Though a diagnosis system is a suitable solution to detect and identify faults, it is first important to ensure the diagnosability of the system: will the diagnosis system always be able to detect and identify any fault, without any ambiguity, when it occurs? In this paper, we present an approach to identify and integrate faults in a model of a technological system. Then we use these models for the diagnosability study of faults by characterizing their observable behaviors.